How can you comply with the latest emissions regulations for diesel trucks? Many options use alternative fuels. Those needing the most power for heavy-duty operations find diesel the fuel of choice for the foreseeable future. That's because diesel has the greatest energy density per gallon.
Controversy exists among manufacturers about how to meet 2010 standards. Four engine makers—Cummins, Detroit Diesel, PACCAR, and Volvo/Mack—rely on exhaust after-treatment, a process called selective catalytic reduction (SCR). Navistar's International MaxxForce engines use an “in-cylinder solution” to control nitrogen oxides (NOx). It's a marketing war of the words, as each system has vocal proponents.
What lowers particulate matter (PM) increases NOx. Strategies to lower NOx increase PM. Higher combustion temperatures burn diesel more completely, but in the confines of the engine's cylinders, high temperature fuses nitrogen and oxygen to form NOx.
Exhaust gas recirculation (EGR) dilutes oxygen-rich air with inert exhaust. That lowers combustion temperature to control NOx. Since 2007, diesel particulate filters (DPFs) remove PM.
SCR uses urea to convert NOx back to nitrogen and oxygen, allowing more complete combustion. It reduces PM and improves fuel economy. Being downstream of turbochargers, SCR doesn't contribute to underhood heat.
SCR engines comply with 2010 re- to 0.2 grams/quirements, limiting NOx hp-hr. SCR reduces re-circulated exhaust to improve mileage 4% to 6%.
Navistar has opted to save the cost, weight, and complexity of after-treatment by using Advanced EGR. EGR levels are increased, but advances in fuel and air management limit PM to control DPF clogging.
The bad news: Navistar achieved 0.5 grams/hp-hr NOx, short of the 0.2 gram goal. The good news: Navistar had enough credits with the EPA to be certified as compliant for 2010 and will be through 2012.
Navistar cites fuel economy gains comparable to SCR engines. According to Tim Shick, Navistar's director of business and product strategy, advanced fuel management slows the burn rate which lowers NOx. Shick reports that Navistar is testing 0.2 gram compliant engines now, pending EPA certification.
The fuel story
Alternative fuels have incentives for use. Closest to diesel but spark-ignited is natural gas, available in compressed or liquid form. Energy density is 60% of diesel. Compressed natural gas (CNG) from delivery pipes is compressed, stored, and pumped into vehicles. After compression, it is about 1% of its original volume, at about 3600 psi for a full tank.
When chilled to -260° F, gas liquefies and condenses to about 1/600 of its original volume. Liquefied natural gas (LNG) is delivered and stored in cryogenic tanks, like Thermos bottles, and pumped into similar truck tanks.
Both CNG and LNG offer a price advantage over diesel on a gallon-equivalent basis, but because of tank size and weight, range is limited. Both types burn more clearly than diesel.
Hybrid vehicles combine conventional power with a means of recovering kinetic energy during braking, and using it when under extra load. Diesel/ gas/gasoline-electric hybrids have motors that double as generators, assisting braking and recharging batteries. When extra power is needed, generators become motors.
Hydraulic fluid can be used in hybrid heavy trucks. Kinetic energy is converted to hydraulic pressure stored in tanks, then released to supplement engine power for acceleration. All hybrids save fuel by capturing and re-using kinetic energy rather than wasting it as brake heat.
Propane and biodiesel are in their infancies. Although propane has been around for years, companies such as Roush Clean Tech are developing medium-duty Ford F series trucks with 6.8 Liter V-10 propane-fueled engines.
Biodiesel from renewable oils, with glycerin removed, show reduced greenhouse gas levels compared to petro diesel. Engine makers now allow up to 20% biodiesel.
Paul Abelson is a former director of the Technology and Maintenance Council of the American Trucking Association and is on the Board of Truckwriters of North America. E-mail firstname.lastname@example.org.
Learn more at World of Concrete
World of Concrete attendees can hear about green engine technology firsthand, at the New Technologies for Greenhouse Gas & Fuel Economy Regulation Compliance event.
The session will feature presentations on current engine options, future technology developments, and regulatory issues that affect the development of clean, advanced technology vehicles. Also, find out how your fleet can comply with new EPA and DOT fuel efficiency and greenhouse gas standards, and meet members of the Hybrid Truck Users Forum.
The event takes place Wednesday, Jan. 19, from 2 – 4 p.m.; $20 online or onsite. Sponsored by the CALSTART clean transportation consortium. More details at www.worldofconcrete.com.